Ultraviolet radiation and the INTERSUN Programme

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Health effects of UV radiation

UV health effects on the immune system

The immune system is the body’s defence mechanism against infections and cancers, and is normally very effective at recognizing and responding to an invading micro-organism or the onset of a tumour. Although the data remain preliminary, there is increasing evidence for a systematic immunosuppressive effect of both acute and low-dose UV radiation exposure.

Animal experiments have demonstrated that UV radiation can modify the course and severity of skin tumours. Also, people treated with immunosuppressive drugs have a greater incidence of squamous cell carcinoma than the normal population. Consequently, beyond its role in the initiation of skin cancer, sun exposure may reduce the body’s defences that normally limit the progressive development of skin tumours.

Several studies have demonstrated that exposure to environmental levels of UV radiation alters the activity and distribution of some of the cells responsible for triggering immune responses in humans. Consequently, sun exposure may enhance the risk of infection with viral, bacterial, parasitic or fungal infections, which has been demonstrated in a variety of animal models. Furthermore, especially in countries of the developing world, high UV radiation levels may reduce the effectiveness of vaccines. Since many vaccine-preventable diseases are extremely infectious, any factor that results in even a small decrease in vaccine efficacy can have a major impact on public health.